1. Field of the Invention
The invention relates to a cord switch and a detecting apparatus using the same, and more particularly, to a cord switch for detecting that an article or a human body is caught (stuck) or almost caught (stuck) in an automatic door or the like and a detecting apparatus using the same.
2. Description of the Related Art
For example, in several types of vehicles, a sensor is installed at a tip end of a door using an automatic switching mechanism such as a power sliding door, back door, or the like, so as to detect a condition of the article or the human body when the article or the human body is caught or nearly caught between mechanical parts such as the door and the car body, and to reversely move the door in an opening direction when the abnormality is detected.
A cord switch has been proposed as a sensor for realizing the above object.
So-called “cord switch” is a pressure sensitive cable switch for sensing the pressure alteration to switch the ON/OFF-state of the automatic switching mechanism. The “cord switch” is typically a contact type cable switch (contact cable). They maybe also called as a cord-like switch or a cable-type pressure sensor.
A contact type cord switch, in which a plurality of wire electrodes come in contact with each other to conduct an ON/OFF operation in response to alteration in a pressure when the article contacts a power window or an automatic door, has been known. For example, such a contact type cord switch is disclosed by a domestic re-publication of PCT international patent publication No. WO97/21235.
FIG. 9 shows a structure of a conventional cord switch disclosed by the domestic re-publication of PCT international patent publication No. WO97/21235. A cord switch 100 comprises a hollowed insulator 101 having a restorability (restorative characteristic), and four wire electrodes 102A, 102B, 102C, 1020 spaced apart from one another at a predetermined interval and spirally arranged along an inner surface of the hollowed insulator 101 in a longitudinal direction.
The hollowed insulator 101 holds the wire electrodes 102 to 102D, in other words, the wire electrodes 102A to 102D are embedded at the inner surface of the hollowed insulator 101 such that the wired electrodes 102A to 102D do not electrically contact with each other. The hollowed insulator 101 comprises a material, which is easily deformed by an external force and restored as soon as the external force is removed, for example, a restorative rubber or a restorative plastic.
The wire electrodes 102A to 102D comprise a metal wire comprising a single wire or a plurality of stranded wires, and a conductive rubber layer or a conductive plastic layer coated on an outer periphery of the metal wire.
FIG. 10 shows a detecting apparatus using the cord switch 100 shown in FIG. 9. In a detecting apparatus 200, a power source 107 and an ammeter 108 are connected in series between a beginning end 104A of the wire electrode 102A and a beginning end 104D of the wire electrode 1020, and a resistor 106 is connected between a beginning end 104B of the wire electrode 102B and a beginning end 104C of the wire electrode 102C. Furthermore, a short circuit line 109A is connected between a terminal end 105L of the wire electrode 102A and a terminal end 105B of the wire electrode 1028, and a short circuit line 109B is connected between a terminal end 105C of the wire electrode 102C and a terminal end 105D of the wire electrode 102D.
In the detecting apparatus 200 shown in FIG. 10, a feeble monitor current i is usually supplied from the power source 107. Therefore, when the external force is applied to the cord switch 100 from the outside, either one of the wire electrodes 102A and 102B contacts with either one of the wire electrode 102C and 102D, as a result a short-circuit current bypassing the resistor 106 is flown, so that the abnormality is detected by sensing an increase of a measured value of the ammeter 106 caused by this current change.
In addition, as another kind of sensor which does not depend on the alternation in pressure, an electrostatic capacitance type sensor is proposed. For example, a non-contact type sensor which detects a risk that the article may be caught in the automatic door, window or the like before contacting the automatic door or window by utilizing an alteration in a floating capacitance or a resistance loss between the article and the electrode has been known. For example, such a non-contact type sensor is disclosed by Japanese Patent Laid-Open No. 2-26414.
However, according to the conventional cord switches, there is a disadvantage in that a detection signal is not output until the hollowed insulator 101 is so deformed that either one of the wire electrodes 102A, 102B contacts with either one of the wire electrodes 102C, 102D, as a result, a considerable force is already applied to the article or the human body when the abnormality is detected. In addition, there is a further disadvantage in that the force applied to the article or the human body caught in the door may be increased, if a closing speed of the door is increased so as to improve the convenience.
Furthermore, the non-contact type sensor disclosed by Japanese Patent Laid-Open No. 2-26414 is inferior to the contact type sensor in regard to a reliability of the detection capacity, since the detection capacity may be varied in accordance with the characteristics, condition, size or the like of the article. In addition, if a detecting range is broadened, the malfunction will easily occur. To the contrary, if the detecting range is narrowed so as to avoid the malfunction, it may be impossible to detect a small article.